The Role of Working Memory and Short-Term Memory in Sentence Comprehension: A Systematic Review and Meta-Analysis in Probable Alzheimer's Disease

The role of either short-term memory (STM) or working memory (WM) in sentence comprehension is a matter of debate. Although it is commonly accepted that memory resources are necessary for sentence comprehension, there is no agreement regarding the nature of their role. The aim of this review is to investigate and synthesize assessment tools and correlation data between STM or WM and sentence comprehension in probable Alzheimer's disease (AD). To this aim, a systematic review and meta-analysis of the literature was conducted according to the PRISMA guidelines. PubMed, Web of Science, Scopus, PsycInfo, and LLBA databases were searched. Two independent authors selected peer-reviewed articles published in English and focused on the relationship between STM or WM and sentence comprehension in probable AD. A total of 11 case-control studies were included at the end of the selection process. Most studies adopted offline tasks to evaluate sentence comprehension, while a small number of authors applied online experimental tasks. The digit span forward and backward were the most employed standardized tests to evaluate phonological STM and WM, respectively. The meta-analysis results supported the association between performance on STM and WM and comprehension tasks. However, moderate heterogeneity was found, mainly due to the small number of included studies, especially for STM, and the substantial variability of the adopted tasks. Therefore, in order to clarify the specific source of language comprehension deficits, new and sophisticated experiments should be conducted using adequate material.